Contour Enthusiasts Group Archives Forums Modifications Zetec Maintenance Wow, getting some idle surging w/ MAF unplugged

Engine runs pretty well above idle. Idle has some misfiring and surges up and down lightly, maybe 50 RPM or so. Tach shows it idling at about 950 RPM, but not sure if tach is accurate since it's a junkyard unit out of a mystique.

So I read about unplugging MAF to put car into limp mode, to kind of rule out MAF problems. It really exaggerated the idle surging... Idle would surge up and down by about 400 RPM.

I believe if you unplug your MAF it should just idle, maybe slightly higher, but still smoothly, right? My idle gets much worse, so I think my MAF sensor is ok and it's time to look elsewhere.

What do you guys think?

can't directly comment as I have a 95 but when I unplugged the MAF once it did just idle smooth but high iirc

Mine idle was going crazy yesterday, almost wanted to die. The wife was like whats going on with the car? I said one sec, pulled over and sure enough the intake popped off. So the maf was connected but nothing being pulled across it so the ECU didn't know WTF was going on. Plus I noticed it was louder

I did have a MAF sensor go, but for some reason the car wouldn't throw the CEL until I took it up on the highway and started doing 45-60mph. Same thing getting it to go off after replacement (didn't wipe the code with the handheld) was on 3 days untill I took it up on the highway again, then it shut off.

You could have it checked for pending codes to see if the MAF comes up.

Before doing anything....go get some electrical parts cleaner and clean the MAF really good.

Thanks, but I've already cleaned up the MAF sensor a couple times very recently. At this point I think it's doing it's job correctly. After all, when it's hooked up, the car runs wayyyy better than it does with it unhooked, so it seems like if anything, it's helping to detect the surging and the computer is able to smooth the idle out some. Maybe that's way off but it seems possible to me.

You know, something that I've noticed recently is a steady increase in vacuum actuator noises inside the car (the motors that control the HVAC options). I just figured it was because everything is getting older and noisier and what not. I wonder if a good sized vacuum leak somewhere in the engine bay could be causing the vacuum motors to move as they receive a varying vacuum signal?

I don't think there's a vacuum leak inside the car because after you shut it down you can still go out there and move the a/c selector switch and you can tell it's still holding vacuum.

hmmmm...

Just for S&G's I would press on electronic sensor connections and main wire harness connections threw out the engine bay, just to make sure they are seated. Make sure you still have the rubber seal inside the MAF sensor connection, might of feel out during a cleaning one time and water/moisture might of got in there.. Double check vaccume even if you think there is no problem, doesn't hurt to look around. A trick to vacumme lines, one is using a throttle cleaner spray, if you hit a leak it should start running ruff, also if you pick up a cheap mechanic stethoscope just pull the metal probe out the rubber tube, so you just have the open tube, and run it along vacumme lines, you should be able to hear the air sucking threw the hose with the hole.

Thanks for the tips... I have to say, I'm not too familiar with the vacuum system on this car. I've seen some lines here and there, mostly EGR firewall lines, etc. but should I be able to hit most of them with the carb spray with everything still in tact on the engine? Seems like to get to most anything, you have to remove half the components, and then it won't run for testing because it's apart

My guess is there's a vacuum leak. Either a hose or the intake manifold gasket. The weird vacuum actuator noises I'm hearing inside the car I think are telling of the problem. Sometimes it almost sounds like water gurgling they are so active... and that's without me touching the HVAC controls. Seems likely with the random missing issue, the surging idle, and the tendency to fall on it's face a little right off idle when I give the throttle a quick jab.

By the way, I have tried a new coil and tested the EGR valve as described here and both checked out just fine. Also replaced the PCV valve. Spark plugs are new, wires are not, but wires gave a perfectly smooth idle on my bro's ZX2, so I think they're ok. Might just have to spring for new ones to make absolutely sure, but money is super tight right now.

Thanks again.

I think if your Hvac controll are leaking, it could cause this. You might want to take a look behind there just to double check.

Yeah access can be a pain with a stock airintake system. I forget how much room I have around the intake manifold because of my CTA (hotair, lol) intake.

I would do a visual inspection of the hoses, that will mean bending and looking for lots of cracks in the hoses. Any one that seems even questionable replace (vacumme hose is cheap) just do one at a time so you don't mix up connections. I would go for the cheap scope and listen as well.

Sometimes if you follow the PCV line to the back side of the engine, that hose has problems. You can see it easy from under the car hooked into the intake manifold.

Thanks again jd.

Good helpful info as always

Np, I just hope it's useful